Method of and apparatus for circulating liquors and vapors in digesters



C. C. HERITAGE El" AL METHOD OF AND APPARATUSFOR CIRCULATING LIQUORS AND VAPORS IN DIGESTERS l Filed Aug. 19, .1935

`mounted in the digester with their lower endsv Patented Feb. 12, 1935 METHOD F AND APPARATUS FOR CIR- CULATING LIQUORS AND VAPORS IN D I- GESTERS Clarklllleritage, Rumford, vMaine, and 'Vance P. l

Edwardes, New York, N. Y.

Application August 19, 1933, Serial No. 685,894

l14 Claims.

This invention relates to a method of and apparatus for circulating liquids and vapors. More specifically this invention relates to a method of and apparatus for the circulation of cooking liq- 5' uors in' pulp digesters.

`In the preparation of paper pulp bythe direct sulphitev cooking process as generally practiced, a pressure cooker or digester is loaded with wood chips and ilooded with a cooking acid preferably introduced at the bottom of the digester. When sufficient acid has been introduced, the vessel is closed and the acid and vchips are gradually brought to the proper temperature and pressure by forcing steam into the digester. The pres'- l5 of relief valves provided for the purpose.

By carrying out the process in this manner,

sure and volume of liquid in the digester are regulated during the vcooking or digesting by meansl it is not possible to` obtain a uniform tempera- ,l

ture throughout the digester and the yield and quality of the.pulp produced varies different parts of the digester.

These objectionable features of the general` cooking process may be overcome by thoroughly circulating Iand agitating thecooking liquor and vapors from the time that the acid is introduced into the digester.

We have now found that we can produce such circulation and agitation by means'of gas cr vaery system. This latter type may be brought into y operation after the digester has been brought `up to rthe proper temperature and pressure.

These vapor lifts comprise pipes or tubes near the bottom Iof the digester. Inside each tube is a pipe of much` smaller diameter having an open end terminating insideand slightly 4above 4 the bottom of the tube through which a gas or vapor to actuate the lift may be introduced. 'I'he external tube of the inside lift terminates slightly above the liquid level in the digester and is 50 preferably bent so that liquor and vapor emitted therefrom will be directed downwardly to the liquor in the digester. The upper ends of the exl ternal tubes of an outside lift do not terminate within lthe digesterv but are connected withthe 55- liquor recovery and vapor relief system located greatly in por lifts. According to our invention, we may outside the digester as will be hereinafter more fully described.

The gas or vapor lifts are caused to operate either by forcing the gas or vapor through the" inside delivery pipe, allowing it to escape at the end of said pipe, or by releasing vapor in the external lpipe at pressures below that maintained I ture is formed which rises-in the external tube because this mixture is less dense than the solid column of liquor surrounding the tube. This operation isvsimilar to the well-known air lift often used by the hydraulic engineer. The outside lifts, furthermore, may be oactuated alone The internal pipe 'is subby maintaining the outside vapor relief system I at a lower pressure thanthe pressure in the digesterthereby causing a ow of liquor from the digester to an outside tank. Vapor is released from this tank and this vapor relief alone isl sufl'icient to operate the outside lifts, as will be. more fully hereinafter described.' l

It is, accordingly, an object of` this invention to provide a process for circulating liquors in dlgesters by releasing a gas or vapor into a column of liquor in the digesters to reduce the specific gravity of the column by forming a gas or vapor-liquor mixture which rises through the column and is discharged either at the top or -out-- side of the digester.

It is a further object of this` invention to provide a process for circulating liquors and 'vapors in vdigesters by maintaining means 'without the digester at lower pressurethan the pressure inside of the digester but at higher elevation whereby circulation` is effected from the digester to the outside means` due to their difference in pressure and whereby part of the liquor circulated may be returned lto the digester by gravity if desired.

It is another object of this invention to provide apparatus for-circulating liquid within a closed vessel for a period of time and then circulate part of the liquor to an outside system without the aid of moving mechanical elements such as fans, pumps and the like.

It is a further object of this invention' to provide a system for circulating liquors and vapors in digestersby means of gas or vapor lifts whereby circulation is maintained inside the digester during the heating' up stage by inside vapor lifts and after the digester is brought up to`the proper domed top 4.

pressure and temperature changing the circula vtion to an outside vapor relief system.

It is a further object of this invention to provide an apparatus for circulating liquors and vapors, in digesters which vincludes liquid dis'- charge tubes immersedin the liquid in the digester and-means for releasing a gas or vaporl into the discharge tube to cause the liquid to be discharged from said tube either at the top of the digester or outside of the digester.

Other and further important objects of this invention will become apparent from the following description and appended claims.

Referring now to the drawing, which discloses a preferred embodiment of our invention, the figure therein illustratedis a front elevation of a digester equipped with the circulating system of this invention, parts of the digester being broken away and the separator in the circulating system being shown in section.

l 0n the drawing;

The improved circulating system of this invention, indicated generally by the reference nuvided with a an'gedfltting 16 providing an opening by means of which the digester is charged with chips and to which is secured a plate i7 for normally closing the digester. The plate Ai7 is provided with a connection'- 18 for a pipe 19 so -that-the pressure in the digester/operates adiaphragm valve 8 in a pipe line 7l supplying SO: and/or steam to the digester.I 'Ihe pressure of the vapor and other gases in the digester is indicated by the pressure gauge 20 mounted on the The digester is supported in a vertical position by means of a plurality of standards or legs 21 secured to the conical bottom 5 by flanged brackets or lugs 22.

The domed top ofthe digester 2 is provided with at least one flanged fitting or connection 23l forming a packing gland for a vertical discharge orn delivery pipe 24 which projects through and linto the digester at a point adjacent the-base of the coned bottom 5. The lower or submerged en d livery pipe 24 and extending substantially the ventire length thereof is a pipe 26, the lower or sub- 1 merged end 27 of which opens slightly above the lower end of the outerlpipe 24. The upper end 28 of pipe 26 isprovided with a laterally extending K steam source 71.

section 29 which extends through packed outlets 30 in the delivery pipe 24 and tting 23. The pipe section 29 is connected to a pressure operated diaphragm valve 70 which valve is connected with a sulphur dioxide, sulphur dioxide and steam, or

trolled valve 34 'the purpose of which will bev more fully hereinafter described.

A vertical discharge or deliverypipe 8f) is `'amounted entirely .within the digester 2 as shown.

The lower end of the pipev is provided with a strainer 81 similar to screen 25. ri'he upper end of pipe 80, however, terminates within the digester above the level of the liquor andmay be provided with an elbow section 82 to direct the liquor discharged through said pipe 80 downwardly toward the liquid level `in the digester represented by dotted line S. The pipe 80 contains an inside pipe 83 which terminates at its lower end slightly above the lower end of pipe 80. Pipe 83 passes through thel domed top 4 through a suitable'packing to prevent leakage and is connected to a' source of steam and sulphur dioxide 7l in a' similar manner to the pipe 26.

A pressure operated diaphragm valve 73 is lo'-x cated in the pipe line 83 between the top of the digester and the steam and sulphur dioxide Y source 71. A pressure relief valve 75 may be connected to the dome 4 of the digester-by means of a pipe 76, on which pipe'a pressure gauge 20 may also be mounted. A pipe 77 leads from the pressure relief valve 75 to the top of the diaphragm in valve 73 andalso to the under side of the dia'- phragm in valve 70. Thus, when the valve 75, which is set at a given pressure, opens, the pressure is transmitted through pipe 77 to the top of the diaphragm in valve 73, thereby closing said valve 73, while at4 the same time the pressure is also Atransmitted to the hunder side of thediaphragm of valve 70 causing said valve to open.

The steam and/or sulphur dioxide from pipe 7l,

instead of being directed into pipe 83, is thusdi.- recd into pipe26 in the digester. This starts the circulationto .the outside vapor relief system through pipe 33 and sets a time valve 34 in operation. f The pressure separator 37 locatel above the digester 2 comprises a closed cylindrical container 38 having a tapered bottom 40 terminating in a anged tubular outlet 4l. The top of the separator is provided with'a flange 42 upon which is secured a domed cover '43. 'I'he cover 43 is provided near the mid-part thereof with pressiue' indicating means 49. A T-tting 46 is secured to ,the closure 43 and is provided with a'pressure vides a support for the pressure gauge 49.

The anged tubular outlet 4l of the preure separator is provided with a closure 50 having a connection 51 for-a pipe section 52 leading back to the digesteras shown. A valve 63 in the pipe section 52 may be used to control the ilow back to thedigester. 'This valve, however, need not be used in `normal operation.

- A constant liquor level R is maintained by means of a float actuated liquor relief device connected to the anged tubular outlet '41 of the pressure separator 37 by means of a pipe section 91. The constant level device 90 contains a oat actuated valvei 92 which automatically opens` when the liquid level is raised above R, allowing this liquor to discharge through'pipe 94feither to an acid recovery system, or to the sewer.

A pipe line 64 having a valvel 67 isprovided in the side of the digester near the top for taking samples and also for emergency relieving liquor from the digester. Y

The piping arrangement of the circulating system described Aabove may,l of course, be varied from that disclosed without materially reducing the effectiveness of the system. For example,V

either inside or outside lifts may be used thruadditional inside and outside lifts may be used in` the digesterif desired.

In the operation of ourldevice, wood chips are introduced vinto the digester 2 through the opening in the tting 16. Thechips are then flooded with acid injected into the digester through the acid line to a height indicated by the broken `line S. At the same time the inside lift 80 is brought into operation by introducing steam, sulphur dioxide or a mixture of sulphur dioxide and steam through pipe 71. 'I'he mixture of sulphur dioxide gas and steam may be obtained from another digester as vapor relief. from a central evaporator handling both relief gas and liquor,

Vfrom a steam lactuated injector pulling yvapor off ofthe outside separator of another digester or steam alone may bel introduced from a boiler, since the liftvmay be operated'by steam alone. Circulation of liquor and vapors is thus maintained within the digester during the entire heat- `ing up stage so that the contents of the digester are always in a state of constant ebulli'tion' and so that uniformity of composition and of` temperature throughout the digester is always maintained. During this stage of the operation, of

course, valve 73 is open and valve 75 is closed. 'I'he circulation is maintained, according to the principles of the well-known airlift, by forcing:

the sulphur*I dioxide and/or steam through the pipe 83 and releasing it at the bottom of the pipe 83 which terminates slightly above the bottom of the discharge'pipe 80. The gases and liquor form a mixture which is less dense than the solid column of liquid outside of the pipe 30.` This 'mixture therefore raises in the pipe 80 and is f disand decreases or shuts off the supply of steam and/or SO2 in pipe 71. This does -not however stop the outside lift from functioning as the pressure difference between the digester and sepa.-`

rator is sumcient tov'cause continuous release of vapor in the lift and the lift continues to func- This pressure difference continues to exist sincev tion so long as this pressure difference exists.

the separatoris constantly receiving vapor and yliquor at a predetermined automatically controlled rate thru valye 34 and is maintained at a lower pressure than the digester by pressure relief valve 48 and the digester pressure is maintained by pressure regulating valve 8 controllingv the admission of steam and/or S02. l The valve 8 in the supply line 71 may also be thermo-operated by the temperature in the discharge line 33. Thereby either the pressure within the digester or the temperature of the discharg Vthe differential pressure between the gas pressure in the digester and inthe separator and cause a continuous flow from the separator to the digester. In this way liquor constantly circulates from thevdigester into` the separator by vapor lift action and. from the separator back into the digester by gravity. The constant level device 90 removes the equivalent volume of steam and considerable vapor added thru the lifts and keeps the system from getting too full of liquid.

It is to be understood that the pressureI in separator 37 may be so regulated that the cir- ;culation ofthe liquid from the digester can be effected without forcing sulphurdioxide or steam through pipe 26. Thus the ilow of vapor and liquor from the digester tothe separator can be entirely brought about due tothe difference in pressure acting on the liquid column in and partially manipulate temperature pressure and liquor concentrations as may be required in the pulping process, water and SO2 being constantly added and/or removed from the digester.

It will thus'be appreciated that by constructing a device operating somewhat on the principle of an air lift, we are able to greatly improve the eiiiciencyof pulp cooking processes by providingfor a constant circulation of the cooking liquor in the` pulp digesters.

While we have disclosed a preferred embodiment of our invention, it is to be understood that we do not propose to be limited thereto, as it is apparent that various details of construction maybe varied without departing from the spirit of the invention disclosed.

We claim as our invention:

l. Apparatus for circulating liquid in pulp digesters, comprising in vcombination a pressure cooker having a liquid therein, a vertical pipe projecting' into said cooker and having an open end submerged the liquid therein, means for injecting av gas into the submerged end of said pipe to thereby decrease the effective density of the liquid in saidpipe and cause it to flow therefrom, means for receiving said liquid and separating the gas therefrom, and means for returning the liquid to said cooker.

' 2. Apparatus for circulating liquid in pulp digesters, comprising in combination a pressure cooker having a liquid therein, a vertical delivery pipe projecting therein with a substantial part thereof submerged in the liquid in said digester, a gas pipe in said delivery pipe, means for forcing a gas therethroughand into said delivery pipe to thereby decrease the specific gravity of the liquid in said pipe and cause it to ow from said cooker, a receptacle for receiving said discharged liquid and separating the gas therefrom, and means for returning the liquid to said cooker.

3. Apparatus for circulating liquid in pulp di.

gesters, comprising in combination a' pressure cooker having a liquid therein, a vertical delivery pipe projecting into said cooker with a substantial portion submerged in the liquid therein, a gas pipe arranged in said delivery pipe,

-4. The process of circulating cooking liquors in digesters, which comprises confining a column of the cooking liquor in the digester, releasing a gasinto the column of liquor to decrease the effective specific gravity thereof whereby the column is discharged'from the digester by the hydrostatic head of cooking liquor therein, collecting the discharged liquor and returning it to the digester.

5. The process of circulating cooking liquors in digesters, which comprises confining a column of the cooking liquor in the digester, forcing sulphur dioxide into said confined liquor column to decrease the effective density thereof whereby the columnis discharged from the digester due to the hydrostatic head of the cooking liquorv therein, collectingl said discharged liquor, separating the entrained sulphur dioxide therefrom and returning the liquors to the digester.

6. The process of circulating cooking liquors in digesters, which comprises confining a column of liquid therein, injecting a stream of sulphur dioxide and steam into said column at the base thereof to decrease the effective density of the liquid column and thereby cause it to be dis,

charged .from the digester by the hydrostatic head of the -cooking liquor in the digester, collecting the discharged liquor, separating the sulphur dioxide therefrom and returning the liquor to the digester.

'1. Apparatus for circulating liquids in pulp digesters,` comprising in combination, a pressure `cooker having a liquid therein, a vertical pipe projecting into said cooker having an open end submerged in the liquor therein, the upper end of said vertical pipe being connected to a tank l `wherein vapors andthe liquid rising in the pipe are separated, a relief valve on said tank to maintain pressure therein lower than the pressure in the-digester, a'liquid return pipe from said tank to the digester and float operated means to remove part4 of the liquid from circulation.

8. 'I 'he process of. circulating cooking liquors in digesters which comprises confining a column of the cooking liquor in the digester having an open end near the bottom thereof and an upper end connected with an outside tank maintained at a lower't pressure ,than said digester whereby liquid and vapors are caused to flow from the digester to the tank due to vapor lift and the decrease in pressure, separating the liquid from the vapors in said tank and returning part or all` of the liquid to the digester. v

9. A device for circulating liquldand vapors in digesters, comprising in combination with a digester, means mounted in' said digester partially. submerged in and opening in to the liquid therein, means forforcing gas -into said first means: near the submerged end to thereby decrease the specinc gravity of the liquid in said rst means and Vromeni cause it to ow together with said gas toward the top of said digester to be there discharged, means similar to said rst means for directing said gaseous liquid mixture from said digester to an outside receiver and means for returning part of.

the liquid from said receiver to said digester.

l0. The process of circulating liquid and vapors in a digester which comprises confining a plurality of columns of the liquid in the digester, flowing the liquid through said columns from the bottom to the top thereof, regulatingthe now through the said columns by the pressure.

within the digester and discharging some of the liquid from the digester for a predetermined period to prevent ooding.

spective pipes, va receptacle for receiving some -of the liquid from said pipes and separating the gas l or vapors therefrom and means for returning the liquid to lsaid cooker. v

12, In an apparatus of the class described,'in combination, a pressure cooker, an outside re'- ceptacle in communication therewith, a vertical column in said cooker having anjopen end near f the bottom of the cooker and-an open top near the top of the cooker, a second vertical column in said cooker having an open end near the bottom thereof, a pipe connecting the top'of said second column with said receptacle, means'for releasing a gas or ,vapor in said columns near the bottoms thereof to lift the confined liquid in the columns, means controlled by the pressure within the cooker for operating the release means and automatically controlled means for regulating the ow of the lifted liquid from the second column to the receptacle. f c

13. In an apparatus of the class described in combination, a pulp digester, a vapor and liquid separator in communication therewith, an inside vapor lift inside the digester, a second vapor lift in said digester communicating with the separator, a valve controlled by pressure within the to said vapor lifts, automatically controlled means for regulating the discharge from the second vapor lift to the separator and means for returning part of the liquid in the separator tothe digester.

14. The process of circulating liquid and vapors in pulp digesters which lcomprises confining 'a column of the liquor in thev digester, 'flowing the liquor in said column from the bottom to the top thereof, confining a second Icolumn of the liquor in said digester, flowing the liquor in said second kcolumn to an outside receptacle for a predeter- 1 mined period, separating gases or vapor from the liquid flowed into said receptacle, and returning part of the liquid to the digester.

CLARK c. HERITAGE.'

vANcE P. EDWARDES.

1g 11. Apparatus for circulating liquids and vapors Y in digesters which comprises a pressure cooker 

